1. Field of the Invention
The present invention relates to microdevice manufacturing and in particular relates to systems and methods of manufacturing microdevices in a manner that reduces co-linearity effects.
2. Description of the Prior Art
Microdevices are miniature apparatus that perform a specific function on a small scale (typically 1 mm or less). Examples of microdevices are micro-electro-mechanical devices (MEMS), digital mirror devices (DMDs), ink jet arrays and thin-film magnetic read/write heads used in magnetic recording systems for data storage.
In magnetic disk drive systems, data is read from and written onto the recording media utilizing a thin-film read/write head. Typically, one or more recording disks are mounted on a spindle such that the disks can rotate and a read/write head is mounted on a movable arm to be positioned closely adjacent the rotating disk surface of each disk to read or write information thereon.
During operation of the disk drive system, an actuator mechanism moves the read/write head to a desired radial position on the surface of the rotating disk where the magnetic head reads or writes data. The head is fabricated on a block material referred to as a xe2x80x9cslider.xe2x80x9d Typically, a slider is formed with an aerodynamically shaped surface that is mounted parallel to the recording disk surface, and forms an air-bearing surface (ABS) during operation. The magnetic head device is contained on a surface normal to the ABS surface and at the trailing end on the slider where the gap between the slider and the recording media is a minimum.
The manufacture of microdevices such as thin-film read/write heads involves the use of lithographic techniques very much like those used to fabricate integrated circuits (ICs) on a semiconductor substrate (wafer). Presently, steppers and scanners with wavelengths ranging from the mercury i-line to 248 nm to 193 nm are used. By way of example, thin-film magnetic read/write heads are typically formed as a two-dimensional array of device units on a ceramic wafer. After wafer-level processing of the device units is complete, the substrate is then sliced into row-bars, with each bar comprising a row of unfinished slider units. One of the sliced edges of each row-bar is then lapped to form a smooth surface, which precisely intersects the magnetic throat of each head on the row bar.
With reference to FIG. 1A, there is shown a cross-sectional view of an inductive thin-film head having a top pole 2A and a bottom pole 2B separated by an insulating region 3. Write coils 4 pass through insulation region 3 and carry a current that induces a magnetic flux, F, in poles 2A and 2B. Poles 2A and 2B come together to form a throat 5 with an end 6 that scans over a magnetic media 7.
With reference now to FIG. 1B, when throat 5 is too long, the magnetic flux leaks out between the extended poles through insulation layer 3, which weakens the flux available for writing in magnetic medium 7. On the other hand, with reference to FIG. 1C, when throat 5 is too short, the air path between end 6 and magnetic medium 7 is large and presents a high resistance that weakens the magnetic flux at the write plane. Thus, the throat length is a critical dimension in the functionality of a thin-film head.
With the assistance of electrical test structures, which are located next to the heads, it is possible to hold much tighter tolerances on the throat position (and thus throat length) using lapping than would be possible using lithography. However the result of the lapping depends upon the colinearity of the images that determine the throat position, since the lapping operation produces a straight edge that cuts across the row of devices. Thus any randomness in the position of the devices inevitably results in an error in the position of the throat and thus an undesirable degradation in device performance. Optional subsequent steps may form features on the lapped surface such as the air bearing surface using a plasma etching processes.
After the ABS processing is completed, the row-bar is then further diced into s individual sliders, each slider having at least one optical or magnetic head terminating at the slider ABS.
As the dimensions of thin-film read/write head devices continue to shrink, the allowable co-linearity error also shrinks. The lapping operation can be controlled very accurately, but randomness in the position of each device on the wafer limits the performance and yield of the devices. This randomness in position is primarily the result of the properties of the particular lithography system used to fabricate the device. The main error contributors include pattern placement errors on the mask, distortion in the imaging lens, and stitching errors.
With regard to stitching errors, the field size of a lithography tool is usually about half the length of a typical row-bar, so that two or more exposure fields (each of which contains a two-dimensional array of microdevices) must be stitched together. Stitching errors include overall placement variations in each field (stepping errors) as well as any rotation errors between the mask pattern and wafer pattern. The net result is an unavoidably large error budget for the position of the devices in a row-bar measured normal to the lapped surface. These errors are typically on the order of 30 to 50 nm and are referred to as xe2x80x9cco-linearity errors.xe2x80x9d Co-linearity errors determine the most critical performance properties of the thin film head device.
Though co-linearity errors have been described with respect to thin-film read/write head devices, these errors are generally present in the fabrication of microdevices where exposure fields must be stitched together to form a complete device, or where another operation such as lapping must be performed on a number of device fields. Reducing co-linearity errors in the fabrication of microdevices results in higher yields and better device performance.
The present invention relates to microdevice manufacturing, and in particular relates to systems and methods of manufacturing microdevices in a manner that reduces co-linearity effects.
In particular, the present invention is a method of printing the critical levels of a microdevice, such as a thin-film read/write head. The method includes using a mask having at least one column of microdevice patterns. Only one of the columns need be illuminated. An accurate stage is used to move the workpiece normal to the direction of the column before printing the next column and subsequent columns. Reducing the number of columns to be printed per exposure to a single column minimizes position variations in the column direction of a row of devices (e.g., a row-bar) that cuts across all columns. By positioning a row-bar across such a row, the microdevices are positioned very repeatedly in the column direction and the subsequent lapping operation can optimally control a critical device parameter, i.e., throat height.
Accordingly, a first aspect of the invention is a method of fabricating microdevices from a workpiece. The method includes the steps of illuminating a single column of microdevice cells on a mask with pulses of radiation. This may be achieved by providing a mask with a single column of microdevice cells, or by illuminating a single column of a mask having many columns of microdevice cells. The method also includes the step of patterning the workpiece with images of the illuminated single column to form corresponding adjacent columnar exposure fields by continuously moving the substrate in the direction perpendicular to the long axis of the columnar exposure fields during illumination of the mask so that each columnar exposure field is formed by a single pulse of radiation.
A second aspect of the invention is a system for patterning a workpiece to form microdevices in a manner that reduces colinearity effects. The system includes a radiation source for providing pulses of radiation and a radiation source controller in operation communication with the radiation source for controlling the emission of the radiation pulses from the radiation source. An illuminator arranged to receive pulses of radiation from the radiation source and illuminate a single column of microdevice cells on a mask. A projection lens is arranged to receive pulses of radiation passing through the mask and is adapted to form a columnar exposure field of microdevice units that corresponds to the column of microdevice cells on the mask. The system also includes a workpiece stage capable of supporting the workpiece and moving the workpiece over a scan path relative to the projection lens and in a direction normal to the projected direction of the column on the workpiece. A workpiece stage position control unit is in operable communication with the workpiece stage and in communication with the radiation source control unit. The workpiece stage position control unit controls the movement of the workpiece stage over the scan path such that a single pulse of radiation forms a single columnar exposure field, with temporally adjacent radiation pulses forming adjacent columnar exposure fields.